1. Field of the Invention
The present invention relates generally to cushioning devices, such as shock absorbers, for cushioning movement between two relatively moveable structures. More specifically, the present invention concerns a cushioning device that is particularly suitable for use as a tow bar in a trolley-type conveyor system (e.g., a power and free conveyor system).
2. Discussion of Prior Art
A moving structure is likely to experience shock (e.g., sudden acceleration or deceleration), and it is often desirable to absorb and cushion the shock so that untoward loading and consequential wear or damage of the structure is avoided. Accordingly, movement of the structure is often cushioned relative to some other structure. This is typically accomplished by providing a cushioning device between the two structures. However, traditional cushioning devices present numerous problems.
These problems are particularly evident in conveyor systems having a series of load carriers that are routinely stopped along the length of the conveyor system. It will be appreciated that such conveyor systems are often used in assembly lines and stoppage of the load carriers permits various steps to be performed at assembly stations spaced along the conveyor line. Furthermore, the carriers will often support large, heavy items (e.g., an automobile) and stoppage of the carriers must account for the momentum of not only the carrier but also the item supported thereon. It is also noted that starting and stopping of the load carrier at each of the stations is typically sudden so as to provide, among other things, less travel time between stations.
One example of such a conveyor system involves a so-called "power and free conveyor system", wherein a power track provides power to the conveyor system and the free track carries the loads and is selectively coupled to the power track for moving the loads along the conveyor path. The free track traditionally includes a load carrier comprising a drive unit that is selectively connected to the power track, a load-supporting unit for supporting an item, and a tow bar interconnecting the units. Traditionally, the drive unit is simultaneously disconnected from the power track and stopped, which consequently requires the load-supporting unit and the item supported thereon to suddenly decelerate. It is important that this shock be absorbed so that damage to the conveyor system and item is avoided. It is also important that the absorbed energy is not stored (e.g., as would normally be the case when a spring is used to absorb the energy); otherwise, the stored energy will likely cause the carrier to lunge forwardly which can be damaging to the conveyor components and supported item and dangerous.
The tow bar used in a traditional power and free conveyor system consequently includes structure that attempts to absorb the shock loads between the drive unit and the load-supporting unit. However, it is believed that conventional tow bars are simply incapable of effectively diffusing the shock loads between the drive and load-supporting units. Moreover, conventional tow bars often have complex and/or expensive constructions and fail to provide the durability needed in most conveyor system environments. Furthermore, a tow bar is preferably adjustable so that the various ranges of shock loads can be accommodated; that is to say, a tow bar preferably permits user adjustment of the amount of resistance it provides to relative movement between the drive and load-supporting units. It will be appreciated that such adjustability permits the tow bar to be used with various load sizes (i.e., the tow bar can be used with variously sized items carried on the load-supporting unit). However, it is also believed that most conventional tow bars designed to permit adjustment of the shock absorption, in fact, provide little, if any, effective adjustability.